(R)-(−)-5-[2-[[2-(2-ethoxyphenoxy)ethyl]amino]propyl]-2-methoxybenzenesulfonamide is known as Tamsulosin. Presently Tamsulosin is being marketed as its hydrochloride salt under the Trade name FLOMAX. It is an α-adrenergic antagonist used preferably for treating benign prostatic hyperplasia.
U.S. Pat. No. 4,703,063 describes two processes for the preparation of Tamsulosin, one of which involves the conversion of a hydroxy substituted analogue of Tamsulosin, i.e., a compound having the Tamsulosin structure but contains a hydroxyl substituent at a position α to the benzenesulfonamide ring, by halogenation followed by reduction and the other involves condensation of an appropriately substituted benzyl methyl ketone with the substituted phenoxy amine, followed by reduction of the resulting imino compound.
The above described processes are non-stereospecific and the final product requires an additional step of resolution of enantiomers to specifically obtain (R)-enantiomer tamsulosin.
CA 1,282,077 discloses a process to prepare Tamsulosin wherein (R)-enantiomer of sulfonamide amine has been condensed with ethoxy phenoxy bromide in dimethylformamide to obtain Tamsulosin (Scheme I), which was purified by crystallization before converting into hydrochloride salt.

As per the above described process, Tamsulosin hydrochloride is obtained in low yield, and therefore this process is not suitable for commercial production.
WO 2002/068382 A1 discloses a process to prepare sulfamoyl substituted phenethylamine derivatives including Tamsulosin. The described process involves a coupling reaction between (R)-(−)-5-(2-aminopropyl)-2-methoxybenzenesulfonamide with an acid or a corresponding acid chloride or mixed anhydride to produce Tamsulosin amide and thereafter reduction of the obtained compound gives Tamsulosin. This coupling reaction presents the disadvantage that the acid or acid chloride or anhydride should be provided in a high purity in order to obtain a good yield in the coupling reaction; and it is known in the art that purification of such products is not always easy.
WO 2004/022532 A1 discloses a process to prepare Tamsulosin (Scheme II) wherein protected amine is used during condensation with ethoxy phenoxy derivative to obtain protected Tamsulosin. In this process, an additional step of removing the protecting group to obtain Tamsulosin is involved.

This process involves the use of a protected amine derivative, which needs to be deprotected after the formation of Tamsulosin.
EP 0 380 144 B1 describes a process for preparing Tamsulosin and the like, in stereospecific form, by reaction of a benzenesulfonamide amine with predetermined stereospecificity, with 2-(2-ethoxyphenoxy)ethyl halide, specifically the bromide. In this process, Tamsulosin base has been purified with column chromatography.
WO 2004/016582 discloses a process to prepare Tamsulosin hydrochloride (Scheme III). This process involves two additional steps, first the protection of amine group before condensing with ethoxy phenoxy halide and thereafter the deprotection to obtain Tamsulosin. In all the examples given in this application, column chromatography has been used to purify Tamsulosin base before converting into hydrochloride salt.

In view of the above difficulties, the instant invention describes a new economical and industrially advantageous method to prepare Tamsulosin by using alkaline earth metal oxides as acid neutralizing agent in the alkylation reaction.